@array = (
  [ 1,      2,       3       ],  # <-- $i = 0
  [ 4,      5,       6       ],  # <-- $i = 1
  [ 7,      8,       9       ],  # <-- $i = 2
    ^       ^        ^
    |       |        |
    $j = 0  $j = 1   $j = 2
);